On Significant Discoveries and Landmark Experiments in the Development of Modern Neuroscience

1 On Significant Discoveries and Landmark Experiments in the Development of Modern Neuroscience John DiCecco Department of Electrical and Computer Engineering, University of Rhode Island, Kingston, RI 02881-0805 USA Hermann von Helmoltz, and Ernst von Brücke, would prove Abstract- The methodologies utilized in the contemporary to be the significant “growth spurt” of neuroscience [2]. Their study of neuroscience are manifest from the collective efforts collective efforts to relate biological processes to the fields of of centuries of determined and insightful researchers. From chemistry and physics created a new understanding of the the first query into the most basic of all mysteries, what is a neurophysiologic process. Many of their insights and soul, scientists have struggled to narrow the search in what is discoveries are still valid, proving the true genius of their an ever expansive library of possibilities. The early works of work. Galen, Descartes, and Newton helped focus that attention The roots of the landmark achievements of Bernstein, toward the brain and the elaborate network of Curtis, Cole, Hodgkin, Huxley, and Katz can all be linked to interconnections the brain uses to interface with the outside the tour de force of 19th century biophysics. In turn, the world. Later works of Reymond, Hermann, Helmholtz, contemporary understanding of neuroscience can be attributed Hodgkin and Huxley, and many others, helped form the framework of the current understanding of neuroscience. This to these pioneers, whose work is still considered valid and paper will attempt to explore the contributions of the critical applicable to the currently accepted models of neurobiology. physiological experiments that facilitated the advancement of It is therefore postulated that only marginal advancement in this understanding. It is the further goal of this paper to the true understanding of neurological processes can take establish, by citation of the discoveries throughout the history place without a fair treatment of the history of the science. of neuroscience, that the contemporary understanding of the activation, creation, and conduction of action potentials II. IN THE BEGINNING through neural tissue is valid. The first plenary work on the brain and the suggestion of its function was offered by Galen in 177 C.E. His work with Index Terms— History, neuroscience, neurophysiology, the Barbary ape led to an understanding of many of the electrophysiology, membrane potential, action potential. physiological processes of the human anatomy, including the brain. I. INTRODUCTION The investigation into the action of the brain would have to wait until the 1600s, when a young philosopher and N 159 C.E. a young physician was appointed the personal mathematician named Rene Descartes suggested that the brain I (actually the pineal gland) was responsible for controlling the doctor to Marcus Aurelius, emperor of Rome. He was to care body and mind. He described the body as a machine and the not only for the Emperor but for the gladiators who fought for nerves acted as force transducers. Researchers and scientists, his amusement. Over many years he made tremendous such as Leeuwenhoek and Robert Hooke, discoverer of the contributions to the understanding of human physiology by cell, armed with microscopes and a penchant for discovery, set working mostly with the Barbary ape, and applying those out to identify the mechanisms of this control. discoveries to humans [1]. He would discover that the Among the many contributions Isaac Newton has made to kidneys produced urine by tying the ureter closed and the scientific process, his theory on nerve conduction is the observing the kidney swell. He would go on to discover that most important to the subject of neuroscience. He believed, as paralysis of anatomical structures would result after severing did Borelli and Leeuwenhoek, that nerves were solid and the nerves that controlled them, though he did not fully continuous and his thoughts on electrical pulses propagating understand their functionality. These discoveries seem so through nerves had a profound impact on Luigi Galvani, often st trivial in the 21 century but to Galen, the young doctor, they considered the father of neuroscience. Galvani had used a were revolutionary. Still many others have contributed in this Leyden jar, a predecessor to the modern capacitor, to store manner and the contemporary model of biological processes is electricity from a lightning storm. He then wired the jar to a indebted to their discoveries. severed frog’s limb in a dramatic display of the ability of As with all scientific progress, the advancement of nerves to conduct electricity (figure 1). Though this understanding is not a linear one. The biophysics movement experiment is not the first of its kind, it is generally considered of 1847, led by Carl Ludwig, Émil du Bois-Reymond, 2 to be the first well documented and well executed. however, had been approaching the issue of electrochemical properties from the ionic perspective, hypothesizing that osmotic properties were a result of molecular pores. It would be the work of Julius Bernstein, a student of du Bois- Reymond and assistant to Helmholtz, which would help unify the results of Helmholtz, Reymond and Brücke and define the modern understanding of electrochemical transmission. Bernstein would first need to incorporate the seminal work of Walther Nernst. IV. DIFFUSION, GRADIENTS, AND THE MEMBRANE POTENTIAL Figure 1. Galvani’s frog. The latter part of the 17th century into the early 18th century The work of Wilhelm Ostwald and his artificial semi- spawned a craze for electrical experiments, both for the permeable membrane established the notion of selective relationship to the physiological implications as well as the permeability and that the electrical potential seen at these nature of electricity itself. Ewald Von Kleist and Pieter van membranes was a result of the permeability of ions [4]. Musschenbroek devoted much of their time to the During this time, Walther Nernst, a noted German physicist and chemist, developed the ideas that would eventually lead development of the Leyden jar. With the ability to store him to an electrochemical potential formula, known as the electrical charge, scientists like Alessandro Volta, Charles Nernst equation. He proposed that the equilibrium potential Augustin de Coulomb, Andre Marie Ampere, and Georg across a semi-permeable membrane varies in a linear relation Simon Ohm, set out to describe, in great detail, the ship with the absolute temperature and in a logarithmic mechanisms for the movement of charge [3]. In the midst of relationship with respect to the ionic concentration on either this research, two schools of thought emerged; that of an side of the membrane. In algebraic form animal electricity and that of a two metal electricity. After Volta succeeded in making the first dc battery from discs of ion copper and zinc, the idea of animal electricity was suppressed. RT [ ]outside Eion = ln (1) In 1831 a professor of Physics at Pisa named Carlo zF ion ion []inside Matteucci used a galvanometer to detect a small electrical current from an injured muscle. Of significant importance, where E is the electromotive force, R is the gas constant, equal though not realized at the time, was that the current moved to 8.3145 V C mol-1 K-1, T is the absolute temperature in from inside the injury to the undamaged muscle surface Kelvin, z is the charge of the ion, and F is Faraday’s constant, outside. This single experiment resurrected the work of 9.6485 x 104 C mol-1 . Galvani and the notion that there was indeed “animal It was shortly after Nernst’s publication that Frederick electricity.” The search to explain it was afoot. George Donnan, a British chemist, began working on the issue of ionic distribution across a membrane and the resulting III. THE GOLDEN AGE OF BIOPHYSICS equilibrium. He argued that a membrane was selectively permeable and that the product of concentrations of ions that With the proof of electrophysiological phenomenon came could diffuse through the membrane is proportional on both the burden of proving the mechanisms responsible for its sides of the membrane. [5] That is existence. In a bold initiative, Hermann von Helmholtz, Émil du Bois-Reymond, and Ernst von Brücke formed an RT []ion RT [ion ] ln 12out = ln out . (2) allegiance and adopted as their decree that "no other forces F []ion −F [ion ] than common physical chemical ones are active within the 12in in organism." [4]. Helmholtz, a prominent German physicist, By absorbing the negative into the logarithm and inverting the directly measured the speed of a nerve pulse at 100 ft/sec, well argument of the logarithm, the equation reduces to within the parameters explainable by electrochemical properties.[4] His collegue du Bois-Reymond had postulated, and later established, that nervous impulses were []ion12in ×[ion ]in =×[]ion1out [ion2]out . (3) electrochemical in nature, and traveled much like an electric pulse through a wire. (The comparison of the nerve pulse This is known as Donnan’s Rule and can be applied to transduction to that of telecommunications could hardly be systems in finite volume equilibrium [5]. If however an anion discounted and it is likely that the two fields were mutually that is not permeable with respect to the membrane is present influential.) He was able to observe a temporary decrease in on one side of the membrane, a cation will diffuse through the the “negative variation”, the injury current described by membrane to maintain electrical neutrality. The presence of Matteucci, though he did not realize the significance of this this impermeable anion results in an unequal distribution of discovery. He further proposed that muscles contained diffusible ions. The result is a chemical gradient of specific positive sources and nerves contained negative sinks. Brücke, 3 ions with respect to the two sides of the membrane.

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